Security guard Jessie R. Lewis, critically wounded May 28 in a shooting spree at the International Business Machines data processing center in Bethesda, died yesterday.

His death was the third to result from the 7 1/2-hour siege allegedly mounted by a disgruntled former employe of the computer company.

Lewis, 69, died at 11:30 a.m. at Suburban Hospital of "irreversible brain damage due to multiple gunshot wounds," according to Beth Viehmeyer, a hospital spokeswoman.

Edward Thomas Mann, 38, of Mitchellville, an IBM employe from 1967 to 1979, has been charged with two counts of first-degree murder and 12 of assault with intent to murder.

Larry L. Thompson, 56, and Hung P. Nguyen, 40, both IBM employes, died during the incident in which Mann crashed his Lincoln Continental through the IBM building's glass doors and then allegedly fired 150 rounds of ammunition from four weapons before surrendering.

Lewis was the most critically injured of 10 persons who were hospitalized--eight for treatment of gunshot wounds, one for a stress-related heart attack and one who hit her head after fainting.

Lewis was apparently one of the first victims. His job was to check identification cards of IBM workers and to log in visitors at his station inside the front entrance.

He suffered three bullet wounds, two in the neck and one in the shoulder. He was twice thought to have died, suffering a heart attack at the scene and, later, at the hospital. Doctors said one bullet severed Lewis' jugular vein and passed through the main artery supplying the brain, causing a large loss of blood.

Lewis was a GSA electrician for 32 years, retiring in 1965. After working as a part-time messenger for the American Savings & Loan Association from 1976 to 1979, he went to work full-time for Burns International Security Services in September 1979. He was assigned to IBM lobby security at the Bethesda building two years ago.

"Without a doubt," one Burns official said, "he was very well thought of by the IBM emWashington Post Staff Writer Kenneth Bredemeier also contributed to this story.